Broadband communication systems such as cable modem systems offer users access to fast, high-bandwidth networks. FIG. 1 illustrates a simplified diagram of a conventional cable modem system. The DOCSIS (Data Over Cable Service Interface Specifications) Radio Frequency Interface Specification specifies the transfer of IP traffic, between the cable headend system and customer locations, over an all-coaxial or a hybrid-fiber/coax (HFC) cable network 52. The transmission path over the cable system is realized at the headend by a Cable Modem Termination System (CMTS) 50 and at each customer location by a Cable Modem (CM) 56. The CMTS 50 interfaces the customer with the wide-area network or even metropolitan area network beyond. The DOCSIS standard defines a single transmitter for each downstream channel—the CMTS 50. All CMs 56 listen to all frames transmitted on the downstream channel upon which they are registered and accept those where the destinations match the CM 56 itself or CPEs (Customer Premises Equipment) 58 connected. CMs 56 can communicate with other CMs 56 only through the CMTS 50.
The upstream channel is characterized by many transmitters (i.e. CMs 56) and one receiver (i.e. located within the CMTS 50). Consider the case of two cable modems (CMs) that belong to different cable segments communicating with a single Cable Modem Termination System (CMTS) illustrated in FIG. 2. In the conventional cable modem system operation, each cable modem CM 230 and CM 220 would share a single downstream path to obtain data/signals from the CMTS 210. Also, each cable modem CM 230 and CM 220 has its own upstream path to send data/signals to the CMTS 210. Thus, two upstream frequencies (or one FDMA (Frequency Division Multiplexing) upstream frequency) and one downstream frequency is used by the system of FIG. 2. The CMTS would have a logical port for each CM 230 and CM 220 for the upstream traffic thereto, while having only one port for downstream traffic to both CM 230 and CM 220.
Each CMTS consists of a number of cards of different function coupled together by a midplane. FIG. 3 is an architecture overview of one such CMTS. CMTS 300 has a plurality of line cards 310 (one or two slots wide), which perform the bulk of DOCSIS processing functions, are electrically connected via connectors or other mechanism to a midplane 330. In this example, each of the line cards 310 can support up to 4 downstream channels and 16 upstream channels as well as a number of video channels. Each of the line cards 310 also has a number of connectors to the midplane 330. Each of the line cards 310 has associated with it an I/O card from a group of I/O cards 320. Each of the I/O cards 320 mounts directly behind each line card on the other side of the midplane 330. Each of the I/O cards 320 accepts coaxial cable connections which provide the primary physical layer for cable modem traffic, upstream and downstream. One major problem with such a configuration is the breakdown of one of the line cards, which would necessitate physical repair and reconnect.
To increase the reliability of such a configuration, conventional systems have used coaxial relays in a matrix configuration. These are very expensive, and further, are bulky and cumbersome forcing a matrix design that must be external to the case that packages the CMTS. Further servicing such a system is prohibitive and may lead to a discontinuation in service.
Thus, there is a need for a more effective apparatus to increase the reliability of line cards without the costs associated with a matrix relay.